Re: [Xen-devel] [PATCH] vhd-util create: add -C|nocow option

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2013-11-21 at 14:41 +0000, Ian Jackson wrote:
> Ian Campbell writes ("Re: [Xen-devel] [PATCH] vhd-util create: add -C|nocow 
> option"):
> > On Thu, 2013-11-21 at 15:46 +0800, Chunyan Liu wrote:
> > > Add '-C' (nocow) option to vhd-util create.
> > > 
> > > Btrfs has terrible performance when hosting VM images, even more when the 
> > > guest
> > > in those VM are also using btrfs as file system. One way to mitigate this 
> > > bad
> > > performance is to turn off COW attributes on VM files (since having copy 
> > > on
> > > write for this kind of data is not useful). According to 'chattr' 
> > > manpage, NOCOW
> > > could be set to new or empty file only on btrfs, so add a option here so 
> > > that
> > > users could have a chance to set NOCOW to a vhd image.
> > 
> > Is there not some btrfs (or generic) utility which could be used to do
> > this after image creation rather than trying to build it in to every
> > utility which creates an image file?
> 
> This may seem like a daft question, but why do we even have a vhd
> utility in our tree ?  Is there not some vhd tools package that this
> should be in ?

vhd was originally a microsoft thing and I think most OSS projects
adopted it in an ad-hoc and independent manner.

Most virt solutions have their own tools (e.g. qemu-img and virtualbox's
thing) for these things.

I agree that it seems silly though I'm not proposing to start a separate
project ;-)

Ian.


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